Angiographic estimation of atherosclerotic tissue thickness is important in the determination of atherosclerotic regression or progression in serial angiographic studies. This measurement requires the prediction of non-atherosclerotic arterial taper for the atherosclerotic lumen. I propose to develop methods to estimate atherosclerotic tissue thickness during the progression and regression of atherosclerosis in tapering arteries. Normal arterial taper will be characterized for postmortem human coronary arteries, postmortem rabbit arteries, and rabbit arteries in vivo. Preliminary data supports the use of this animal model since the change in arterial width due to branching has been found to correspond to the findings for postmortem human coronary angiograms. Both are predicted by a formula derived from the principle of minimum work. The change in arterial width due to branching can be estimated along the artery with the estimated normal diameter of one segment and of the branches. The difference between the atherosclerotic lumen and the non-atherosclerotic taper represents atherosclerotic area. This approach seems justified since coronary artery disease is known to progress from proximal to distal in the main lumen and in branches. The measure will be tested during atherosclerotic progression and regression in rabbits recorded by serial angiography and will be confirmed by postmortem findings. It will be applied to the estimation of human coronary atherosclerotic wall thickness by the evaluation of postmortem angiograms. The estimates will be confirmed by histological measurements of wall thickness. The method will then be applicable to the grading of human coronary angiograms.